This invention relates to the control of diffused-air bubbles in ink-jet print cartridges for the purpose of ensuring acceptable operation of the cartridge irrespective of whether the cartridge is stored for a significant period of time prior to use of the cartridge.
An ink-jet printer typically includes one or more cartridges that contain ink. In some designs, the cartridge houses separate reservoirs of more than one color of ink. Each reservoir is in fluid communication with a printhead that is mounted to the body of the cartridge.
The printhead is controlled for ejecting minute drops of ink though orifices on the printhead to a printing medium, such as paper, that is advanced through the printer. The cartridge is usually scanned across the width of the paper while the printhead ejects a swath of ink droplets onto the paper. The paper is advanced between scans. The ejection of the drops is controlled so that the swaths of printed ink combine to form recognizable images on the paper.
Although the printhead is a reliable and efficient means for ejecting ink droplets, it carries no mechanism for preventing leakage of ink through the orifices when the printhead is not operating. Therefore, ink supplied to the printhead is contained under a slight partial vacuum or back pressure. The back pressure is large enough to prevent the free flow of ink from the printhead, but not so large as to prevent an activated printhead from expelling ink. This range can be considered the printhead""s back pressure operating range.
Some types of ink-jet cartridges use porous material such as synthetic foam to contain the ink within the reservoir. The foam is nearly completely saturated with ink. Unsaturated portions of the foam provide the capillarity for holding the ink in the reservoir in the desired back pressure operating range.
The ink reservoir of such a cartridge includes a chamber for storing the foam. The reservoir also includes a standpipe into which the ink flows from the chamber. No foam is in the standpipe. Ink stored in the standpipe flows through a feed slot that is continuous with but relatively smaller than the standpipe. The feed slot thus connects between the standpipe and printhead to deliver the ink to the printhead.
A fine-mesh filter is mounted to the standpipe at the junction of the foam and the standpipe. The filter prevents any solid debris or large air bubbles from moving into the standpipe. The foam is compressed against the filter-covered end of the standpipe. The standpipe protrudes somewhat into the ink chamber, so that the foam compression against the filter is localized there to create a relatively high capillarity in the region of the foam nearest the filter. This high capillarity ensures that ink stored in the foam near the filter will be drawn to and through the filter, and that a liquid (ink) seal will be maintained at the filter until all of the useable ink in the foam is delivered into the standpipe.
The print cartridge filling process may leave some residual amounts of air in both the foam and the standpipe. Also, a certain amount of air is dissolved in liquid ink, which is typically water based. Some of this dissolved air will leave solution and collect as bubbles in the foam and the standpipe. Air that collects in the foam can be vented to ambient. To this end, some of the walls that define the ink chambers may be configured to provide a series of connected relief pockets adjacent to the foam. As explained in U.S. Pat. No. 5,671, 001, which is assigned to the assignee of the present application, such pockets provide a practical means for removing air bubbles trapped in the foam, which bubbles might otherwise expand (especially when the cartridge is subjected to external temperature and pressure variations) by an amount sufficient to force ink to leak from the printhead orifices.
A small air bubble that is normally present in the standpipe after the cartridge is filled does not affect the operation of the print cartridge. That is, the bubble is not large enough (relative to the volume of the standpipe) to occlude ink flow through the standpipe. Such occlusion would cause the printhead to fail in a manner analogous to a pump that loses its priming liquid. Thus, this type of printhead failure is often referred to as xe2x80x9cde-priming.xe2x80x9d
Over time, the air bubble in the standpipe may grow. Minute amounts of air will diffuse from the atmosphere through the foam containment and filter and into the standpipe. The air coalesces with any residual air in the standpipe to form what can be characterized as a diffused-air bubble.
The growth of the diffused-air bubble in a standpipe can affect the shelf life of a print cartridge. Under certain conditions the diffused-air bubble in a stored print cartridge can eventually grow to a size that occludes ink flow to the printhead and cause the printhead to de-prime shortly after the cartridge is installed and used.
The present invention is directed to a method and apparatus for controlling the growth of diffused-air bubbles in ink-jet print cartridges for the purpose of ensuring a satisfactorily long shelf life of the print cartridge.
Embodiments of the present invention provide a method of retarding in time the growth of a diffused-air within the standpipe. This delays the occurrence of a diffused-air bubble that is large enough to occlude ink flow to the printhead, thereby extending the shelf life of a print cartridge.
As one aspect of the invention, there is provided a mechanism for increasing the distance (hence, the time) that diffusing air must travel before reaching a location in the standpipe where it can coalesce into a diffused-air bubble. A spacer is mounted in the standpipe to accomplish this in one preferred embodiment of the invention.
Apparatus and methods for carrying out the invention are described in detail below. Other advantages and features of the present invention will become clear upon review of the following portions of this specification as well as the drawings.